Dehydration provokes a variety of cardiovascular and endocrinological events to maintain blood pressure and prevent further fluid losses and also stimulates drinking to replace those losses. These physiological and behavioral effects are coordinated by the brain. In the rat, drinking behavior is specific to the type of dehydration: if only water is lost, the rat drinks mainly water; if both water and sodium are lost, the rat drinks both water and salty water. Many cues help direct this behavior, but the renin-angiotensin-aldosterone hormonal system is especially important in the elicitation of salt appetite and sodium conservation during sodium need. This goal of this research is to define the brain receptor areas involved in both the stimulation and inhibition of salt appetite. Different series of experimentally with peripheral angiotensin converting enzyme inhibition and with sodium depletion, will examine the interaction of mineralocorticoid and angiotensin in drinking and salt appetite at different specific sites in the brain, and will attempt to define a site of action for atrial natriuretic peptide in the inhibition of salt of action of atrial natriuretic peptide in the inhibition of salt appetite. The methods use a combination of techniques including intracerebral tissue microinfusions with agonist or blocking drugs, selective electrolytic lesions, and chemical lesions. The brain areas of greatest interest are the subfornical organ, the organum vasculosum laminae terminalis, and subnuclei of the median preoptic nucleus, all of which contribute to the overall control of both physiological and behavioral events regulating body fluid balance and blood pressure.